In general, as a radiator used in an antenna or a feed portion therefor in a communication field for a millimeter wave band or a quasi-millimeter wave band, a slotted waveguide radiator is used as a radiator which can radiate electromagnetic waves efficiently.
As shown in FIG. 16, the slotted waveguide radiator is constituted such that slender slot 2 is provided so as to be coincident with a flow direction of magnetic flux F generated at a broad side plate 1a by electromagnetic wave P propagating inside a waveguide 1 with a rectangular section thereby radiating the electromagnetic wave externally.
Incidentally, the intensity of the electromagnetic wave radiated from the slot 2 externally depends on the magnitude of the magnetic flux F at a position where the slot 2 is provided.
The magnitude of the magnetic flux F becomes larger as it is farther away from the central line C of the broad side plate 1a. 
Further, the magnetic flux F is generated so as to turn inversely at intervals of ½ of waveguide wavelength λg.
Accordingly, for example, in case that electromagnetic waves with the same intensity and the same phase are radiated from a plurality of slots provided in a waveguide, it is necessary to consider attenuation and phase of the electromagnetic waves propagating inside the waveguide due to radiation form respective slots.
For this reason, as shown in FIG. 17, a plurality of slots 21, 22, . . . 2n are provided about the central line of the broad side plate 1a in a staggered manner at intervals of ½ of a waveguide wavelength λg and setting is made such that distances r1, r2, . . . rn from the central line C of the broad side plate 1a become larger as the slots become farther from an input end of the electromagnetic wave P.
As the slotted waveguide radiator which radiates electromagnetic wave on the basis of such a principle, there are one having a single waveguide array structure where the plurality of slots 21, 22, . . . 2n are provided along the lengthwise direction of the waveguide 1 at predetermined intervals, as described above, so that a radiation face serving as a radiator are widened in the lengthwise direction of the waveguide 1, one having a single waveguide single slot structure where only one slot is provided, or one having a planar structure where the radiators having the above-described array structure are provided in parallel so that a radiation face serving as a radiator is expanded in its lengthwise direction and in a widthwise direction.
The slotted waveguide radiator having the above-described single waveguide array structure can be used, for example, as a feed portion for feeding electromagnetic wave with the same phase to one side of a dielectric base board of a planar antenna such as a dielectric leaky-wave antenna or the like.
Further, the slotted waveguide radiator with the above-described planar structure can be used as a planar antenna for a quasi-millimeter wave band or a millimeter wave band as it is.
As a method for manufacturing such a slotted waveguide radiator, a method for performing integral molding by an injection molding is conventionally employed regarding the above-described single waveguide array structure.
Furthermore, in the slotted waveguide radiator with the planar structure, as shown in FIG. 18, a method for forming a plurality of waveguide paths in parallel by providing a plurality of narrow side plates 12 in parallel in a standing manner on a bottom wall 11 having a width corresponding to a plurality of single waveguides and fixing an upper plate 14 which has the same width as that of the bottom plate 11 and is formed with slots 13 in advance is adopted.
In the method utilizing the injection molding, however, since a direction in which a mold for forming a waveguide portion is drawn out and a direction in which a mold for forming a slot portion is drawn out are perpendicular to each other, there is a problem that the molds must be complicated and they can not be manufactured at an inexpensive cost.
Further, as described above, in case of the slotted waveguide radiator used as the feed portion for the dielectric leaky-wave antenna or the like, a H matching plate may be provided in front of a slot for matching with the dielectric base board.
In this case, there occurs a problem that the mold for forming a slot portion can not be released due to interference with the matching plate so that the matching plate must be formed as a separate member.
On the other hand, as described above, in the method for constituting a planar type slotted waveguide radiator by providing a plurality of narrow side plates 12 on the bottom plate 11 in a standing manner and fixing the upper plate 14 above them, since the performance of the radiator deteriorates due to leakage of electromagnetic waves even if there are slight gaps between upper and lower edges of the plurality of narrow side plates 12, and the lower plate 11 and the upper plate 14, there occurs a problem that much labor and time are required for connecting work for these members.
On the other hand, as a prior art which can solve the problems as described above, IEICE Trans. COMMUN., VOL. E84-B, NO. 9 SEPTEMBER 2001, pp 2369-2376, “Millimeter-Wave Slotted Waveguide Array Antenna Manufactured by Metal Injection Molding for Automotive Radar Systems” by Kunio SAKAKIBARA, Toshiaki WATANABE, Kazuo SATO, Kunitoshi NISHIKAWA, and Kazuyuki SEO is known.
That is, the millimeter wave slotted waveguide array antenna according to the prior art is constituted with waveguide slots where 45° slanting slots are provided on narrow faces of waveguides stacked in a two stage manner through broad faces at intervals of λg/2 in a staggered manner regarding the upper and lower waveguides, and a feed portion for performing feeding of the two waveguides with opposite phases.
In the prior art, however, there is a problem that the feed portion for performing opposite phase feeding is complicated and distances between the slots become large in the slanting direction, large grating lobe occurs in this direction, and it is difficult to secure a size accuracy required for millimeter wave in a molding.